Breast cancer is a significant health problem for women in the United States and throughout the world. Although advances have been made in the detection and treatment of the disease, breast cancer remains the second leading cause of cancer-related deaths in women, affecting more than 180,000 women in the United States each year. For women in North America, the life-time odds of getting breast cancer are now one in eight.
No universally successful method for the treatment or prevention of breast cancer is currently available. Management of breast cancer currently relies on a combination of early diagnosis (e.g., through routine breast screening procedures) and aggressive treatment, which may include one or more of a variety of treatments, such as surgery, radiotherapy, chemotherapy and hormone therapy. The course of treatment for a particular breast cancer is often selected based on a variety of prognostic parameters including an analysis of specific tumor markers. See, e.g., Porter-Jordan and Lippman, Breast Cancer 8:73-100 (1994).
Although the discovery of BRCA1 and BRCA2 were important steps in identifying key genetic factors involved in breast cancer, it has become clear that mutations in BRCA1 and BRCA2 account for only a fraction of inherited susceptibility to breast cancer (Nathanson, K. L. et al., Human Mol. Gen. 10(7):715-720 (2001); Anglican Breast Cancer Study Group. Br. J. Cancer 83(10):1301-08 (2000); and Sydjakoski K., et al., J. Natl. Cancer Inst. 92:1529-31 (2000)). In spite of considerable research into therapies for breast cancer, breast cancer remains difficult to diagnose and treat effectively, and the high mortality observed in breast cancer patients indicates that improvements are needed in the diagnosis, treatment and prevention of the disease.
MicroRNAs are a class of small, non-coding RNAs that control gene expression by hybridizing to and triggering either translational repression or, less frequently, degradation of a messenger RNA (mRNA) target. The discovery and study of mRNAs has revealed miRNA-mediated gene regulatory mechanisms that play important roles in organismal development and various cellular processes, such as cell differentiation, cell growth and cell death (Cheng, A. M., et al., Nucleic Acids Res. 33:1290-1297 (2005)). Recent studies suggest that aberrant expression of particular miRNAs may be involved in human diseases, such as neurological disorders (Ishizuka, A., et al., Genes Dev. 16:2497-2508 (2002)) and cancer. In particular, misexpression of miR-16-1 and/or miR-15a has been found in human chronic lymphocytic leukemias (Calin, G. A., et al., Proc. Natl. Acad. Sci. U.S.A. 99:15524-15529 (2002)).
The development and use of microarrays containing all known human microRNAs has permitted a simultaneous analysis of the expression of every miRNA in a sample (Liu, C. G., et al., Proc Natl. Acad. Sci U.S.A. 101:9740-9744 (2004)). These microRNA microarrays have not only been used to confirm that miR-16-1 is deregulated in human CLL cells, but also to generate miRNA expression signatures that are associated with well-defined clinico-pathological features of human CLL (Calin, G. A., et al., Proc. Natl. Acad. Sci. U.S.A. 101:1175-11760 (2004)).
The use of microRNA microarrays to identify a group of microRNAs, which are differentially-expressed between normal cells and breast cancer cells (i.e., an expression signature or expression profile), may help pinpoint specific miRNAs that are involved in breast cancer. Furthermore, the identification of putative targets of these miRNAs may help to unravel their pathogenic role. The present invention provides novel methods and compositions for the diagnosis, prognosis and treatment of breast cancer.